The invention relates to fuel cells. More particularly, the invention relates to materials for fuel cell cathodes. Even more particularly, the invention relates to methods of making materials for fuel cell cathodes.
Polymer electrolyte fuel cells (PEFCs), including direct methanol fuel cells (DMFCs) have attracted great interest as an alternative power source for vehicles and portable electronic devices. Factors that significantly reduce the efficiency of DMFCs include sluggish methanol oxidation at the anode, sluggish oxygen reduction reaction (ORR) at the cathode, and methanol crossover. The sluggish methanol oxidation and ORR cause a large overpotential at the anode and the cathode, respectively, thus dramatically reducing cell voltage. Methanol crossover is the permeation of methanol through the solid electrolyte membrane from the anode to the cathode, where it is oxidized. The simultaneous ORR and oxidation of methanol at the cathode lead to an additional reduction of the cathode potential and decrease in DMFC performance.
Platinum and platinum-based metal alloys are, at present, the most widely used ORR catalysts in DMFCs. Efforts have been made to develop alternative ORR catalysts other than platinum that are either inactive or sufficiently tolerant to methanol. Nano-cluster MoxRuySez and RuxSey compounds, for example, have been prepared from ruthenium carbonyl precursors in the presence of organic solvents, such as xylenes. Such methods require the use of toxic carbonyl complexes and organic solvents. While aqueous routes to the production of such catalysts have been reported, such methods require the use of potentially toxic materials, such as elemental selenium, as well.
Methods of making highly active, methanol tolerant cathode catalysts currently employ organic solvents, as well as other potentially toxic materials, or both. Therefore, what is needed is a method of making fuel cell catalyst materials that is carried out in aqueous solution without the use of toxic materials. What is also needed are high efficiency electrode catalysts that are made by such a method.